306 FRAGMENTS OF SCIENCE 



rest by the beautiful researches of Wells. I do not think 

 that any boy of average intelligence will be satisfied with 

 the simple answer that the dew falls. He will wish to 

 learn how you know that it falls, and, if acquainted with 

 the notions of the middle ages, he may refer to the opin- 

 ion of Father Laurus, that a goose egg, filled in the morn- 

 ing with dew and exposed to the sun, will rise like a 

 balloon a swan's egg being better for the experiment 

 than a goose egg. It is impossible to give the boy a 

 clear notion of the beautiful phenomenon to which his 

 question refers without first making him acquainted with 

 the radiation and conduction of heat. Take, for example, 

 a blade of grass, from which one of these orient pearls is 

 depending. During the day the grass, and the earth be- 

 neath it, possess a certain amount of warmth imparted by 

 the sun; during a serene night, heat is radiated from the 

 surface of the grass into space, and, to supply the loss, 

 there is a flow of heat from the earth to the blade. Thus 

 the blade loses heat by radiation, and gains heat by con- 

 duction. Now, in the case before us, the power of radia- 

 tion is great, whereas the power of conduction is small; 

 the consequence is that the blade loses more than it gains, 

 and hence becomes more and more refrigerated. The light 

 vapor floating around the surface so cooled is condensed 

 upon it, and there accumulates to form the little pearly 

 globe which we call a dew-drop. 



Thus the boy finds the simple and homely fact which 

 addressed his senses to be the outcome and flower of the 

 deepest laws. The fact becomes, in a measure, sanctified 

 as an object of thought, and invested for him with a 

 beauty for evermore. He thus learns that things which, 

 at first sight, seem to stand isolated and without apparent 



